The purpose of this study was to examine how Whole Exome Sequencing (WES) has been used since it became clinically available in late 2011 by describing the demographics and prior genetic testing of the population receiving this test, and examining how those factors relate to the test result and clinical presentation of the patients. An additional goal was to examine if the diagnostic yield and demographics had changed significantly over time in the two years of data collection. A de-identified dataset of 499 cases of WES performed by Ambry Genetics was evaluated. It was determined that diagnostic yield did not significantly vary over time, and at 26%, was consistent with prior reports12. Gender distribution was approximately equal with 54% of cases male and 46% female. The majority of cases (83%) were pediatric and the age at time of test authorization ranged from prenatal to 86 years of age. A disparity was observed in the ethnic distribution of cases. Of those WES patients with information on ethnicity, 85% were described as being Caucasian. A significant correlation was observed in the number of single gene tests performed prior to WES and the WES result. Those with more single gene tests were more likely to get a positive result from WES. The most frequently reported organ system involvement included neurological (64%) and musculoskeletal (55%). The most commonly selected overall health category was mental retardation/ intellectual disabilities/ developmental delays (MR/ID/DD) seen in 64% of all WES cases.